Optical fiber characterization measurements can include, for example, fiber span length, Stimulated Raman Scattering (SRS) measurements, dispersion measurements, loss measurements, etc. The conventional approach to fiber characterization involves out-of-service measurements with test equipment and/or estimates based on calculations (e.g., loss and dispersion determined based on length, fiber type, etc.). The out-of-service measurements are time-consuming, costly, and error-prone (e.g., loading measured data into planning tools, spreadsheets, etc.). Also, the out-of-service measurements may not reflect future conditions when an optical system is in-service. As optical networking systems continue to evolve with higher capacity, there is a need to get as much margin and performance as possible out of the system including having exact fiber characterization measurements for configuring the optical networking system accordingly.
The fiber span length measurement is the physical length of a fiber span. One conventional approach looks to physical route distance such as based on a map, Global Positioning Satellite (GPS), etc. Another conventional approach includes estimating the length of a fiber span in an optical system using an Optical Time Domain Reflectometer (OTDR) trace and identifying the end of the fiber based on observed events or performing a Round-Trip Delay (RTD) measurement using an Optical Service Channel (OSC). The RTD measurement requires sending a data packet from node A to node B, on one fiber, returning that packet to node A on a second fiber, then comparing the timestamps of the outgoing and returning packets. The fiber length can be determined from the timestamps and the speed of light. Using an OTDR trace, it is generally difficult or impossible to unambiguously identify the end of the fiber as it may not be a clear signature in the OTDR trace. For example, in a long span, a low reflection event corresponding to the end of the fiber could be below the noise floor of the OTDR and therefore not detectable. RTD measurements have limited accuracy (+/−5%) because of timing jitter of the OSC packets. Also, RTD measurement assumes that the two fibers have equal length, which may not always be the case.
The fiber SRS measurements relate to fiber nonlinearity. Conventionally, the fiber nonlinearity coefficient or effective area (Aeff) of the fiber is simply derived from the fiber type information, which is extracted from a database or entered manually in a network design tool. There is no known commercial equipment to perform this type of measurement. Fiber type information is often unreliable as it is usually entered manually. It can also be confusing if mixed fiber types are present in the same fiber span and difficult to combine. Patch panel losses are often ignored or entered in the design tool as a default rather than a measured value. This can result in a large uncertainty in terms of determining the optimal channel launch power in each span based on nonlinear measurements.
The fiber dispersion measurements can be performed in the field using commercial test equipment. However, in many cases, fiber dispersion is derived from the fiber type information, which is extracted from a database or entered manually in a network design tool. The use of commercial test equipment is costly and time-consuming. Further, the commercial test equipment may not be available when needed and it needs to be physically transported to the ends of each fiber span.